Well, Pop Century is brightly colored, and has giant coke cups and bowling pins and stuff. I guess that would appeal to kids. But it in no way compares to the GF, which has much bigger rooms with balconies, queen beds, the monorail, much nicer pools, a beach, better food options, and is mere minutes from the MK. It also has organized activities for kids, and easy access to other resorts with kids activities, like FW. There's a wide variety of recreation options - boat rentals, bike rentals, etc.
I've stayed at Pop, and enjoyed it. It's a very, very nice motel, but it's still a motel. Double beds, no balconies, very small rooms, need to keep your curtains closed all the time because your only window opens out onto a walkway. Food court only, no sit-down restaurants. The pools are nicely themed, but there's no slide, and no zero-entry area like the GF has. Bus transportation only.
If the GF is within your budget, there's no question. Go with GF.